Lipid metabolism is essential for all cells and most likely every developmental process, and yet many questions remain regarding mechanisms of lipid processing and transport. The Farber lab uses the developing zebrafish to study the roles of long-chain acyl-CoA synthetases (Acsls) and fatty acid transport proteins (Fatps), enzymes that process and transport long-chain and very long-chain fatty acids. My long term goal is to understand the role of one of these proteins, fatty acid transport protein 2a (Fatp2a), during zebrafish development and ultimately in human physiology. Fatp2a is an ortholog of human Fatp2, an enzyme that both transports long-chain fatty acids across membranes and activates very long-chain fatty acids into fatty acyl-CoAs. My preliminary studies demonstrate that loss of Fatp2a in zebrafish larvae profoundly attenuates primitive red blood cell development (erythropoiesis). Interestingly, fatp2a transcript is primarily expressed not in the site of primitive erythropoiesis, but in the yolk syncytial layer (YSL). Because the YSL surrounds the yolk cell and expresses many genes important for lipid absorption, metabolism, and packaging (Marza et al 2005;Farber et al, unpublished), we believe the YSL acts to absorb lipids from the yolk and package them for delivery to the developing embryo. The proposed studies will test the hypothesis that Fatp2a activates or transports a specific fatty acid from the yolk that is necessary for proper primitive erythropoiesis. The following specific aims will help elucidate the nature of the phenotype and reveal the substrate that Fatp2a activates and/or imports to influence erythropoiesis. I will explore the role of Fatp2a in proliferation, migration and maturation of erythroid cells by using different staining techniques and in vivo time-lapse microscopy. I will explore the requirement for Fatp2a in a cell autonomous or non-autonomous manner by microinjecting antisense reagents and mRNA in a tissue specific manner as well as creating transgenic fish lines. Finally I will reveal Fatp2a's substrate using mass liquid chromatography/mass spectroscopy. The preliminary data, coupled with the proposed experiments will address a new and unexpected role for Fatp2 activity in regulating blood cell development. These results will not only increase our knowledge of this important developmental pathway, but may have clinical implications for the treatment of devastating blood diseases like some leukemias.